Embodiments of the present technique relate generally to switching devices, and more particularly to methods and systems for enhancing performance of micro-electromechanical systems (MEMS).
MEMS are electromechanical devices that generally range in size from a micrometer to a millimeter in a miniature sealed package. The near zero power consumption, small size, high isolation, switching speeds, linearity, low distortion and low insertion losses achievable by MEMS devices make them ideal for implementation in a plurality of application spaces. Accordingly, MEMS devices find wide usage, for example, in pressure sensors, actuators, displays, gyroscopes, bio sensors and various radio frequency (RF) transmission circuits.
A conventional MEMS device in the form of a micro-switch may include a movable actuator, such as a cantilever beam that moves towards a stationary electrical contact. Particularly, the movable actuator moves under the influence of a gate driver typically positioned on a substrate below the movable actuator. To that end, the gate driver employs electrostatic, magneto-static, piezoelectric and/or thermal designs for providing actuation forces that facilitate the movement of a free end of the movable actuator towards the stationary contact to complete the electrical circuit.
The extremely high isolation and the extremely low “on-resistance” of the MEMS switch, however, cause a dramatic change of state while opening or closing the MEMS switch. Such sharp electrical transitions may cause a transfer of energy across the contacts causing damage or failure of the MEMS switch, which in turn, degrades the system performance. Accordingly, to mitigate such conditions, certain approaches describe the use of power diverters and active circuits for reducing the energy that couples across the MEMS contacts during opening or closing of the MEMS switch. Such approaches, however, are typically expensive and may not be suitable for certain application environments.
Another mitigation technique employs specific circuit configurations that temporarily bypass the current into a secondary electrical path. Such a technique, although useful when opening the MEMS switch into flowing current, may not be appropriate for use in applications where only a limited current is available during the opening and closing of the switch. By way of an example, in receiving and transmitting circuits for devices such as magnetic resonance (MR) coils of a Magnetic Resonance Imaging (MRI) system, the voltage across a switch is drastically reduced as the transmit pulse is off during the operation of the switch. The surrounding gradient fields in the MR system, however, may induce voltages on the MR coils due to magnetic and electrostatic coupling. Accordingly, the gradient fields may cause voltages, for example, of about 1 Volt (V) to appear across contacts of the MEMS switch. Switching in an out of such voltages stresses the MEMS switch, often leading to damage or failure of the MEMS switch and/or the MR system.
It is desirable to develop methods and systems that greatly improve the MEMS reliability by reducing the energy coupled across the contacts during opening and closing of the MEMS switch. Additionally, there is a need for MEMS switch configurations that provide high isolation, yet prevent self-actuation or failure especially in application environments prone to strong electromagnetic fields, voltage and current surges, and fast transients.